1. Field of the Invention
This invention relates to a process for preparing organic alcohols, aldehydes, and ketones comprising selectively oxidizing alkanes and aromatics using as a catalyst certain iridium complexes. More specifically, the oxidation process involves using an iridium metal catalyst complex with the iridium being coordinated with the nitrogen atoms of a benzimidazolyl-containing ligand.
2. Description of the Related Art
The oxidation of saturated hydrocarbons e.g., alkanes, particularly cycloalkanes, with active oxygen such as molecular oxygen or air to produce the corresponding alcohol, ketone and/or acid reaction product(s), has been an area of research activity for many years in view of the utility and environmental benefits of the reaction to the chemical industry.
There are a number of reports in the literature of various ways to oxidize hydrocarbons to the corresponding aldehyde or ketone. One reference is U.S. Pat. No. 5,958,821 B1 which discloses oxidizing various hydrocarbons such as cycloalkanes, aromatic hydrocarbons, etc. with oxygen in the presence of an oxidation catalyst comprising imide compounds such N-hydroxyphthalimide and a metal compound co-catalyst such as cobalt or manganese acetyl acetonate. The patentee of the '821 reference enumerates virtually every class of known hydrocarbons and virtually every metal in the periodic table.
Other references which have addressed the oxygenation of alkanes include Shun-Ichi Murahashi et al. in J. Chem. Soc., Chem. Commun., (1993) 139-140 in which the authors present results for the oxidation of alkanes and alkenes with oxygen in the presence of aldehydes and using a copper compound catalyst. Their results showed that linear alkanes such as N-decane had extremely low conversion. In Catalysis Letters 8 (1991), 45-52 the same authors have shown that isobutane can react with oxygen in the presence of an iron perhaloporphyrin complex to give mostly tert-butyl alcohol.
Shun-Ichi Murahashi et al. have reported in Tetrahedron Letters, vol. 34(8), (1993) 1299-1302, the ruthenium catalyzed oxidation of alkanes with alkyl hydroperoxide. Specifically, they reacted n-heptane and n-decane to provide ketones and alcohols., G. P. Khirnova et al. in Petrol. Chem. U.S.R.R. vol. 21(1), 49-52 (1981) have reported the liquid phase oxidation of isobutane using a heterogeneous catalyst containing cobalt and molybdenum borides or molybdenum carbides. The main products of this reaction were tert-butyl hydroperoxides, tert-butyl alcohol and acetone. It has also been shown in U.S. Pat. No. 5,395,980 B1 that isobutane can be converted to tert-butyl hydroperoxide at elevated temperatures (about 140° C.) by reacting it with oxygen in the presence of tert-butyl alcohol and di(tert-butyl) peroxide.
There are also reports of the oxidation of alkanes with oxygen using N-hydroxyphthalimide (NHPI) as a catalyst and a metal compound co-catalyst. For example, Y. Ishii et al. in Catalysis Surveys from Japan 3 (1999) 27-35 report the oxidation of various alkanes including isobutane. The isobutane gave tert-butyl alcohol and acetone and tert-butyl hydroperoxide. The other alkanes which were tested were all branched alkanes. No results are presented for the oxidation of n-butane using NHPI as the catalyst. Ishii et al. in J. Org. Chem. (1996) 61, 4520-4526 present results of the oxidation of various cycloalkanes using NHPI and Co(acac)n. Results are also presented for the oxidation n-octane to give octanols and octanones.
The research continues in this area. Improved processes and more effective catalysts for the processes would be of great benefit to the industry.